Secure communications networks, including audio communication facilities, which are available only to authorised users, are well known for use, for example, by defence services, by police or by financial or commercial enterprises. However it is a frequent requirement of a user of a terminal on such a secure network also to have access to open, unsecured networks or to networks with a lower level of security, or for users on such a lower security or unsecured network to have access to a user on a secure network. Referring to FIG. 1, to avoid any possibility of digital data passing from a first network 1 to a second, less secure, network 2, a known solution is to provide a user 3 of a secure network 1 with two terminals, a first terminal 10 connected to the secure network 1 and a second terminal 20 connected to the less secure or unsecured network 2. The two terminals may be housed in a same cabinet or housing, possibly with a shared microphone for use on both networks, but effectively two separate and mutually isolated terminals need to be provided to the user. This doubling of equipment is clearly an expensive solution to the problem of preventing digital data passing between the networks both in terms of the initial provision of terminals and in their maintenance.
There is another known variant of this solution that involves a “mediator”, as follows. When a first operator needs to talk with a second operator at another site, the first operator approaches a first mediator at the first operator's site to inform the first mediator that information is required from the other site, with which the first operator does not have security clearance to communicate.
The first mediator contacts a second mediator at the other site and the second mediator communicates with an analyst at the other site and information from the analyst is relayed via the mediators back to the first operator. However, often multiple mediators are involved to allow requests to work up through security levels, which is clearly inefficient and subject to error.